This application claims the benefit of Korean Application No. 99-39331, filed Sep. 14, 1999, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical recording/reproducing apparatus, and more particularly, to a method of determining a direction in which an optical pick-up moves, and detecting a track cross signal used as a basis of determining tracking pull-in after searching a track.
2. Description of the Related Art
Track searching of an optical recording/reproducing apparatus means searching for a target track by moving an optical pick-up in a radial direction of a disc. In track searching, the number of moved tracks must be counted in order to determine whether the optical pick-up arrived at the target track. In order to count the number of moved tracks, a track cross signal is necessary. The track cross signal is a pulse generated when the optical pick-up transects a track. That is, it is possible to know the number of moved tracks by counting the pulses generated by the track cross signal. Also, it is necessary to compensate for the number of tracks moved by the eccentricity of a disc. That is, the number of tracks must be increased in a direction, where the influence of the eccentricity increases, but reduced in a direction, where the influence of the eccentricity is reduced. It is determined whether to increase or to reduce the number of tracks using the fact that the phase of a track error signal is inverse to the phase of a track cross signal. Also, the track cross signal is necessary to determine the point of time of the tracking pull-in, after the optical pick-up reaches the target track.
Since the track cross signal is necessary to determine the amount of movement of a track, compensation for the influence of the eccentricity, and the point of time of the tracking pull-in after searching the track, it is important to obtain a correct track cross signal.
In a conventional method, the track cross signal is detected by the envelope of a sum signal generated by a quarter photodetector. However, in a high density optical disc such as an HD-DVD, the width of a track with respect to the size of an optical spot is much smaller than in a conventional CD/DVD. Accordingly, crosstalk caused by an adjacent track is mixed with an RF signal. Therefore, it is not easy to detect the envelope of the sum signal.
FIGS. 1A through 1C show changes in a track error signal and an RF signal according to a track width. FIGS. 1A, 1B, and 1C show the track error signals and RF signals when the optical wavelength is 400 nm, the numerical aperture (NA) of an object lens is 0.6, and track pitches are 0.74 xcexcm (in the case of a DVD), 0.46 xcexcm, and 0.37 xcexcm, respectively.
As shown in FIGS. 1A through 1C, it is difficult to detect the envelope of the RF signal as the track pitch becomes narrower with respect to a uniform optical spot. This is because crosstalk caused by an adjacent track increases due to a narrow track pitch.
Therefore, it is difficult to detect the track cross signal as the track pitch becomes narrower with respect to the optical spot. This means that it is not easy to detect a track in a high density optical disc.
To solve the above problems, it is an object of the present invention to provide an improved method of detecting a track cross signal for a disc having high density narrow tracks.
It is another object of the present invention to provide an apparatus for detecting a track cross signal, which is suitable for the above method.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the first object, there is provided a method of detecting a track cross signal, in which a track cross signal is obtained by binarizing the envelope of an RF signal RF0 obtained by subtracting some light receiving signals generated by some light receiving devices in the radial direction from other light receiving signals generated by other light receiving devices in the radial direction, in a photodetector divided into two sections in the radial direction.
Here, a track cross signal detection signal can be obtained by a quarter photodetector divided in the radial and tangential direction of a disc, a quarter photodetector divided in the radial direction of a disc, or an octal photodetector divided in radial and tangential directions of a disc.
To achieve the second object, there is provided an apparatus for detecting a track cross signal, comprising a radial subtracter for obtaining an RF signal RF0 by subtracting some light receiving signals generated by some light receiving devices in the radial direction from other light receiving signals generated by other light receiving devices in the radial direction, in a photodetector divided into two in the radial direction and a track cross signal generator for obtaining a track cross signal by binarizing the envelope of the RF signal RF0 with the radial subtracter.